Aenert news. Invention analysis
Solid oxide electrolysis technology is based on the high-temperature splitting of water in the form of steam into hydrogen or oxygen. Water vapor is fed into a porous cathode and, under the influence of external voltage, is reduced to H2 + O2− at the boundary with the electrolyte. Oxygen ions pass through the solid electrolyte and are oxidized at the anode to pure oxygen. Hydrogen is collected on the surface of the cathode. The main components in this technology are a negatively charged cathode, where reduction to hydrogen occurs, a positively charged anode, where oxidation occurs, and an electrolyte, which ensures the movement of ions between the electrodes. Solid oxide electrolyzer cell (SOEC) and solid oxide fuel cell (SOFC) have generally the same design and are often combined into a single circuit to ensure operation in electrolyzer or fuel cell modes.
The key characteristics of SOEC include, first of all, the relatively high temperature of the electrolysis process, which is usually in the range of 600-900℃, as well as a ceramic, solid oxide electrolyte. This provides electrolysis by means of SOEC with such important advantages as high efficiency due to accelerated kinetics and high conductivity at elevated temperatures, the possibility of reversible use of SOEC and SOFC, import of heat from external sources, the possibility of producing synthesis gas using carbon dioxide as a raw material.
An invariable requirement inherent in all types of electrolysis is the use of only highly purified fresh water, which in some cases can be a serious problem when scaling up processes. On the other hand, SOEC requires the separation of hydrogen from steam and its purification.
Among the main disadvantages of this SOEC process, first of all, it is necessary to highlight the low service life of the main elements, which is several times shorter than that of alkaline water electrolysis and proton exchange membrane electrolysis. This is due to the high thermal load on the elements of the stack structure, which have different coefficients of thermal expansion, which can lead to loosening and even destruction.
In SOEC designs, the most common cathode material is nickel doped with YSZ (ytrium-stabilized zirconia). Ni degradation in the form of sintering and oxidation are the most vulnerable problems in the operation of such cathodes. Lanthanum-strontium-manganese perovskite (LSM) and other materials are used much less often.
Lanthanum strontium manganate (LSM) is most often used as anode material. However, there are many studies devoted to new anode materials for SOEC, including alloying with rare and rare earth metals, nanoparticles and special manufacturing technologies. High requirements, especially with respect to its density and ionic conductivity, are imposed on the SOEC electrolyte. In this regard, zirconium dioxide doped with YSZ is used here. In addition, materials such as scandia stabilized zirconia (ScSZ), lanthanum gallate and ceria are used.
Currently, the prospects for large-scale commercialization of SOEC are unclear. The share of solid oxide electrolysis on a global scale obviously does not exceed 5-6%, significantly inferior to competitive technologies. However, if new technical solutions appear that can eliminate some of the problems and, above all, increase the durability of electrolytic cells, SOEC will be able to take a worthy place among green hydrogen production technologies.
Below is an overview of recent patents related to SOEC. In total, about 700 patent documents over the past 20 years from 2004 to 2023 were carefully selected for review and statistical evaluation. Several patents that received priority during these years are highlighted and described in detail, which mainly deal with electrode compositions and designs of electrochemical cells.
Among the components of solid oxide electrolysis technology, the most popular among inventors were new designs of electrolyzers, the share of mentions of which in patent documents amounted to slightly more than 38%. In more than 25% of cases, the technical solutions proposed in the inventions related to electrolysis systems as a whole, when the patented innovations cover both the main electrolysis process and the secondary stages of the technological process. SOEC cathodes and anodes were considered in patent documents approximately equally - 13.2% and 12.1%, respectively.
Breakdown of documents by technology elements (left) and technical problems (right). Patents, 2003-2023 (by the number of mentions in patent documents)
Els – Electrolyser; And – Anode; Cat – Cathode; Elct – Electrolyte; Ctls – Catalyst; Ctrl – Control & monitoring;
LEMP – Low efficiency / Main process; LEG - Low efficiency general; LESP – Low efficiency / Secondary process; HCPC – High CAPEX / Plant construction; HCEP – High CAPEX / Equipment production; HORR – High OPEX / Repair & replacement; HOOC – High OPEX / Operation & consumables; HCM - High Cost maintenance; HCG – High Cost general ; ESI – Environmental and Safety issues; UP – Unclear problem
Among the technological problems that inventive innovations were aimed at solving, the following were most frequently mentioned: Low efficiency / Main process – 40% of mentions; High OPEX / Repair & replacement – 19.2%; High OPEX / Operation & consumables – 14%. The proportion of mentions in patent documents of other thematic problems did not exceed 10% for each of them.
Inventions in the form of Device were found in inventions in 50.6% of patent documents. Methods were slightly less popular, being mentioned in 39% of inventions. New Compositions were proposed significantly less frequently over the twenty-year period (10.4%), which indicates the difficulties of patenting this type of technical solutions.
Distribution of patents by type of invention. Patents, 2003-2023 (by the number of mentions in patent documents)
Among the patents in our database devoted to SOEC, the largest number of them were issued by the following patent offices: JPO – 50; USPTO – 47; INPI (Fr) – 39; EPO – 36; CNIPA – 27.
The undisputed leader in the number of patents received was the French Commissariat à l'énergie atomique et aux énergies alternatives (FR). Among other patent holders, Sumitomo Electric Industries, Ltd. (JP), Rondo Energy Inc. (US), Panasonic Intellectual Property Management Co. Ltd. (JP), SunFire GmbH (DE), Toshiba Energy Systems & Solutions Corporation (JP), THU Tsinghua University (CN) stood out.
Several patents issued over the past two years, in our opinion, require special consideration.
Australian patent AU2023250794B2 provides electrode compositions in the form of solid oxide electrochemical cells as electrodes of SOEC or SOFC fuel cells or a reversible solid oxide electrochemical cell.
Bibliographic characteristics of the patent: Current owner - Commonwealth Scientific and Industrial Research Organization CSIRO; Priority - 2022.04.06; Publication - 2024.11.07; Worldwide applications - WO CN EP AU KR; Claims - 60.
The patent authors note that commercialization of SOECs and SOFCs still requires addressing a number of key challenges, including reducing capital costs through low-cost materials and improving electrode performance and lifetime. The invention provides specific electrode compositions that are suitable for scaling while providing control, flexibility, and consistency in electrode manufacturing.
The main feature of the new electrode composition is the inclusion of a plurality of hybrid electrode particles in its composition, wherein each hybrid electrode particle includes at least one metallic phase and one oxide phase. In addition, the metallic phase includes a plurality of metallic particles, and the oxide phase includes a plurality of ionic or mixed ion-conducting oxide particles on the surface of the metallic particles. It is proposed to use silver (Ag), iron (Fe), nickel (Ni) or cobalt (Co) or silver in combination with the above-mentioned metals, as well as with Copper (Cu), and titanium (Ti) as the metallic phase.
Figure 3: Schematic of an electrode composition comprising a plurality of hybrid electrode particles provided as a layer on an electrolyte provided for a cathode of solid oxide electrolysis mode.
The oxide phase may include ion or mixed ion conducting oxide particles selected from metal (e.g. Gd, Sm, Pr, Ni) doped ceria, metal (e.g. Cu) doped ferrites, titanium doped lanthanum strontium ferrite (e.g. LSCF, LSTF), and lanthanum strontium chromium manganese (LSCM). The particle sizes and their ratios are fundamentally regulated in the patent.
Figure 4: Scanning electron microscopy image of a sintered electrode material comprising a silver metal phase and one or more metal doped ceria particles or discrete portions interspersed within the silver metal phase.
The patent details various variants of compositions, methods of manufacturing particles, electrodes and a solid oxide electrochemical cell.
For example, in one of the claims, the sintered electrode material contains a metallic phase as a porous framework and a plurality of discrete oxide phases interspersed in the metallic phase. In this case, the sintered electrode material has a fixed porosity.
Another claim describes a modified salt-gel, for which it is envisaged to prepare an aqueous solution "including an ionic or mixed ionic conductive oxide species, followed by the addition of a chelating agent, a plasticizer, and then metallic species to the aqueous solution."
In addition, the invention describes various variants of the design of electrochemical cells.
According to the authors of the invention, the proposed compositions and designs of SOECs can be successfully used to produce hydrogen by steam electrolysis, as well as other products.
Japanese Patent Application JP2024137341A proposes to patent a fuel electrode for a solid oxide water electrolyzer and a solid oxide water electrolyzer. Current Assignee - Toyota Central R&D Labs Inc; Publication - 2024.10.07; Claims - 7.
The patent document notes, “In water electrolysis using SOEC, high-temperature (700°C or higher) water vapor, which is a raw material, is supplied to the fuel electrode. As a result, Ni contained in the fuel electrode is oxidized to form Ni(OH)2. Since Ni(OH)2 easily evaporates, the morphology of the three-phase interface, which is the site of the electrode reaction, changes due to the evaporation of Ni(OH)2. As a result, the electrolysis performance is deteriorated.”
In order to solve this problem, the patent application proposes "a fuel electrode for a solid oxide water electrolyzer comprising Ni-based particles and electrolyte particles made of a solid oxide acid electrolyte A. The electrolyte particles are made of a solid solution or mixture of Y-doped ZrO2 (YSZ) and Gd-doped CeO2 (GDC). In the present invention, the term "electrolyte particles" refers to particles made of a solid solution or mixture of Y-doped ZrO 2 (YSZ) and Gd-doped CeO2 (GDC).
The following figures illustrate the state of the problem and the mechanism for solving it.
The schematic diagram of a solid oxide water electrolysis cell using Ni/GDC-YSZ as a fuel electrode (active layer) is shown on the left. The schematic diagram of a conventional solid oxide water electrolysis cell (SOEC) using Ni/YSZ as an anode (active layer) is shown on the right. The figures show: 10 - electrolyte layer 12 made of solid oxide electrolyte; 14 - anode attached to one surface of electrolyte layer 12; 16 - cathode attached to the other surface of electrolyte layer 12; 18 - intermediate layer (reaction preventing layer) 18 inserted between electrolyte layer 12 and air electrode 16; 20 - current collector layer of anode side at small anode thickness.
This figure shows that when a solid solution or mixture of a YSZ component and a GDC component is used as the anode, the reaction resistance increase rate decreases depending on the amount of the GDC component. The claims of the invention present a formula for the average composition of the electrolyte particles, and regulate the dimensions, porosity and percentage range of the nickel particles of the fuel electrode.
Patent application EP3978652A1 proposes an Electrochemical cell and hydrogen generation method. The application was published on 21.09.2022. Current Assignee - Panasonic Intellectual Property Management Co Ltd; Worldwide applications - 2020 CN EP WO JP 2021 US; Claims – 13. In January of this year, patent EP3978652B1 was issued based on this application.
According to the text of this invention, the electrochemical cell includes two functionally different cells facing each other through a gas path and containing electrodes and electrolyte layers. However, the electrolyte of the first cell is a conductor of oxide ions, and the second is a conductor of protons. During electrolysis, hydrogen is formed on the first electrode of the first cell, and oxygen is formed on the second. In the second cell, hydrogen is converted into protons on the first electrode, and is converted into pure hydrogen on the second electrode. A schematic representation of the essence of the process is shown in the figures below. As a result of the authors' research, it was discovered that highly concentrated hydrogen can be obtained using a proton conductor. In a conventional electrolyzer arrangement, the electrochemical cell and the capacitor are completely separated and connected to each other by a pipeline, which makes it difficult to miniaturize the system. The proposed technical solution, according to the authors, facilitates the miniaturization of the system.
1A is a perspective view of an electrochemical cell.
1B is a cross-sectional view of the electrochemical cell as shown in figure 1A.
1 - first cell; 2 - second cell; 3 - gas path; 11 - first electrolyte layer; 12 - first electrode; 13 - second electrode; 21 - second electrolyte layer; 22 - third electrode; 23 - fourth electrode; 31 – inlet; 32 – outlet; 100 - electrochemical cell
Hydrogen production via SOEC has a number of problems, one of which is the yield of high-purity hydrogen, the importance of which is commensurate with the problems of the main process. In this regard, the proposed technical solution is of great importance. However, the productivity and final cost of the process, as well as the durability of the elements of the electrochemical cell, are not yet clear.
Of undoubted interest, in our opinion, may be the Chinese patent CN115180937B (Current Assignee - Shanghai University of Electric Power; Publication - 2023.09.22; Claims - 8).
The invention proposes a method for preparing an anode material SOEC with a perovskite structure based on barium ferrite doped with gadolinium and copper. According to the authors, the preparation method effectively reduces the synthesis temperature, effectively stabilizing the cubic phase of the BFO material at medium and low temperatures compared to the prior art. In addition, "the anode material of the cell has excellent electrocatalytic activity, low polarization resistance and low activation energy of interfacial resistance." The invention formula describes in detail the sequence of the proposed technological process, including the compositions of technical solutions, pH values of solutions, modes of obtaining and processing the precursor, temperature parameters of processing, limits of the optimal molar ratio of barium, gadolinium, iron and copper ions, etc.
Chinese patent CN117117208B (Current Assignee - Chengdu Minshan Green Hydrogen Energy Co ltd; Publication - 2023.12.29) proposes a medium-temperature SOFC cathode material doped with lanthanum, a method for its preparation and application. The patent notes that there are several cathode materials that have good electrochemical characteristics and catalytic activity at high temperatures, but at the same time have a number of serious drawbacks. For example, cobalt is a very expensive metal, is characterized by poor structural stability, and has a high coefficient of thermal expansion. The cathode material with a perovskite structure has good thermal expansion and oxygen ion diffusion characteristics, but has low conductivity compared to the same cobalt. As a result, the materials used for medium-temperature solid oxide fuel cells (Intermediate Temperature-Solid Oxide Fuel Cells, abbreviated as IT-SOFC) with an operating temperature range of 600-800℃ are gradually not ideal, which leads, for example, to a decrease in the durability of this type of electrolyzers compared to competitive electrolysis options.
To solve these problems, the patent proposes: “A lanthanum doped intermediate temperature SOFC cathode material is characterized in that the intermediate temperature SOFC cathode material is prepared from Bi 0.5 Sr 0.5 FeO3 As a matrix, la was used for the Bi 0.5 Sr 0.5 FeO3 Doping the A site of (2); the chemical formula of the intermediate-temperature SOFC cathode material is (Bi 0.5 Sr 0.5 ) 1-x La x FeO 3-δ Wherein x is the doping amount of La, 0 < x < 1, and delta is the oxygen vacancy content”. According to the authors of the invention, the proposed material “…has high conductivity and high catalytic oxidation activity, has excellent electrochemical characteristics and can be used as an ideal IT-SOFC cathode material”.
Below we also provide a list of patents that received the highest rating according to our methodology and are part of large patent families:
FR2999612B1 Method for high-temperature electrolysis of steam and another gas, related interconnector, electrolysis reactor and operating methods (Current Assignee - Commissariat a lEnergie Atomique et aux Energies Alternatives CEA; Worldwide applications - 2012 FR 2013 EP JP CA DK US WO; Publication – 2015.02.20, Claims – 21);
FR3056338B1 Methods for co-electrolysis of water and CO2 (SOEC) or production of high temperature electricity (SOFC) which promotes or not catalytic reactions within the H2 electrode (Current Assignee - Commissariat a lEnergie Atomique et aux Energies Alternatives CEA; Worldwide applications - 2016 FR 2017 DK CA JP WO US EP; Publication – 2018.09.21; Claims – 22);
FR3045215B1 Stand-alone system for clamping a high-temperature SOEC/SOFC stack (Current Assignee - Commissariat a lEnergie Atomique et aux Energies Alternatives CEA; Worldwide applications - 2015 FR 2016 DK US EP JP CA WO; Publication - 2023.03.03; Claims - 26).
By the Editorial Board
Energy News Monitoring
Solid Oxide Electrolysis. Recent Inventions
